1. Field of the Invention
The present invention generally relates to the art of producing stitch position data utilized by a sewing machine for forming an embroidery, and particularly to the art of producing stitch position data for forming stitches accurately reflecting the shape of an embroidery area while at the same time largely reducing the number of blocks as divisions of the embroidery area and increasing the degree of freedom as to the shapes of the blocks.
2. Related Art Statement
U.S. Pat. No. 4,388,883 discloses a sewing system which stores embroidery data used for forming an embroidery, with the least possible storage capacity. More specifically, the disclosed system stores embroidery area data including sets of block data each of which is representative of outline segments which cooperate with each other to define a corresponding one of blocks as divisions of an embroidery zone or area to be filled with stitches to provide an embroidery such as an alphabetic character or a figure. The embroidery area data additionally includes stitch density data indicative of a number of stitches formed in each of the blocks using thread. The sewing system automatically produces, based on the block data and the stitch density data, sets of stitch position data representative of respective stitch positions where a sewing needle penetrates a work cloth to form respective stitches filling each of the blocks. A stitch-forming device including the sewing needle, of the sewing system, utilizes the stitch position data for forming respective stitches and thereby providing an embroidery in the embroidery area.
In the event that embroidery area data is prepared for being stored in the above-identified sewing system, generally, an original embroidery area is divided into a plurality of simple blocks such as quadrangles and/or triangles, for forming individual stitches with excellent appearance. When embroidery area data is prepared for, for example, a "leaf" embroidery area 100 as shown in FIG. 23, first, the "leaf" area 100 is divided into a left-hand and a right-hand area, and then the left-hand area is divided into three blocks, B1, B2, B3, and the right-hand area is divided into three blocks, B4, B5, B6. The sewing system prepares the embroidery area data, based on sets of block data for the respective blocks B1 to B6, and stitch density data, and stores the area data.
The set of block data for the block B1, for example, includes four sets of point data representative of four defining points, b11, b12, b13, b14, which cooperate with each other to define four segments, L1, L2, L3, L4, of the outline of the block B1, that is, four vertices defining the four sides of the quadrangle B1. Stated differently, the block B1 is defined by a pair of opposed main outline segments L1, L2 and a pair of opposed secondary outline segments L3, L4 connecting between corresponding pairs of opposed ends of the main outline segments L1, L2. Stitch positions are located on the two (first and second) main outline segments L1, L2. However, in the prior art, under the strict requirement that the (first or second) secondary outline segment L3, L4 which is shared by any adjacent two blocks be defined by a straight line segment, an embroidery area is divided into blocks by determining the number of blocks and the locations of division depending upon the shape of the embroidery area.
The known sewing system stores embroidery area data including block data for the blocks obtained under the above-indicated requirement, and produces, by utilizing the embroidery area data, embroidery data, i.e, stitch position data representative of stitch positions on the main outline segments of each of the blocks. FIG. 23 shows stitches formed by the known sewing system by using the thus produced embroidery data for the embroidery area 100.
Since the prior sewing system is thus required to prepare block data for the blocks whose secondary outline segments are straight line segments, the degree of freedom as to the shapes of blocks which are treated by the sewing system, is insufficiently low. In the event that a character, a symbol (including a logo or a mark), or a figure (representing an animal, a flower, an article, etc.), each having a complex profile whose outline includes a curved or polygonal line segment, is divided into blocks, the embroidery portion defined by the curved or polygonal line segment must be divided into a number of small blocks such that the straight line segments as the secondary outline segments of the blocks sufficiently approximate or match the curved or polygonal line segment. Thus, the number of blocks as divisions of an embroidery area is largely increased, and consequently the total amount of the embroidery area data is increased. In addition, the operation of preparing the embroidery area data is extremely complicated.
Furthermore, since an embroidery area is divided into a number of small blocks and stitches are formed in each of the small blocks, an embroidery as a whole suffers from the problem that the individual stitches thereof do not accurately reflect or represent the shape of the original outline of the embroidery area. In particular with respect to the embroidery area 100 of FIG. 23, adjacent two blocks, e.g., B1 and B4, B2 and B5, etc. are filled with stitches, independently of each other. As a result, a space may be left between the stitches formed in one of the two blocks and the stitches formed in the other block, thereby lowering the external appearance of the embroidery, i.e., quality of the embroidery product.